Preparing the New Phase of Argo: Scientific Achievements of the NAOS Project

Abstract

Argo, the international array of profiling floats, is a major component of the global ocean and climate observing system. In 2010, the NAOS (Novel Argo Observing System) project was selected as part of the French "Investissements d'Avenir" Equipex program. The objectives of NAOS were to consolidate the French contribution to Argo's core mission (global temperature and salinity measurements down to 2000 m), and also to develop the future generation of French Argo profiling floats and prepare the next phase of the Argo program with an extension to the deep ocean (Deep Argo), biogeochemistry (BGC-Argo) and polar seas. This paper summarizes how NAOS has met its objectives. The project significantly boosted France's contribution to Argo's core mission by deploying more than 100 NAOS standard Argo profiling floats. In addition, NAOS deployed new-generation floats as part of three scientific experiments: biogeochemical floats in the Mediterranean Sea, biogeochemical floats in the Arctic Ocean, and deep floats with oxygen sensors in the North Atlantic. The experiment in the Mediterranean Sea, launched in 2012, implemented and maintained a network of BGC-Argo floats at basin scale for the first time. The 32 BGC-Argo floats deployed and about 4000 BGC profiles collected have vastly improved characterization of the biogeochemical and ecosystem dynamics of the Mediterranean. Meanwhile, experiments in the Arctic and in the North Atlantic, starting in 2015 and deploying 20 Arctic BGC floats and 23 deep floats, have provided unique observations on biogeochemical cycles in the Arctic and deep-water masses, as well as ocean circulation variability in the North Atlantic. NAOS has therefore paved the way to the new operational phase of the Argo program in France that includes BGC and Deep Argo extensions. The objectives and characteristics of this new phase of Argo-France are discussed in the conclusion.

Preparing the New Phase of Argo: Technological Developments on Profiling Floats in the NAOS Project

“…Three scientific experiments preparing future extensions of the Argo core array were then carried out: deep floats equipped with dissolved oxygen optodes in the North Atlantic, BGC floats in the Mediterranean Sea, and BGC floats for under-ice applications in the Arctic Ocean. Results of these experiments are described in a companion paper (Le Traon et al, 2020). The project also contributed to strengthening the French contribution to the Core-Argo array thanks to the deployment of more than 100 standard Argo floats.…”

“…Taking these elements into consideration, the autonomy for a Pro-Ice float is estimated at approximately 300 cycles at 1,000 m depthan estimate supported by the 360 cycles of unit WMO4901801, performed daily in the Labrador Sea at the beginning of the project. However, deployments in Baffin Bay have subsequently shown that the number of cycles is actually closer to 200 (Le Traon et al, 2020). This difference could be partly explained by the impact of cold temperatures on the nominal capacity of the battery (estimated loss of between 15 and 20% at 1 • C), but also by an unexpected residual current between the two boards.…”

“…This paper reviews the technological developments carried out as part of NAOS, including in situ validation. A companion paper summarizes the contribution of NAOS to the Core-Argo array and details results from the three scientific experiments (Le Traon et al, 2020).…”

Deep through-flow in the Bight Fracture Zone

“…During the four cruises, CTDO 2 stations were also carried out along the so-called OVIDE line (Fig. 1a) that intersects the Reykjanes Ridge at 58.8 • N, 31.3 • W (Lherminier et al, 2007). Here, we consider the stations on the eastern side of the Reykjanes Ridge, from 27.2 to 30.7 • W, to analyze the along-stream evolution of ISOW upstream of the BFZ.…”

The Oceans’ Biological Carbon Pumps: Framework for a Research Observational Community Approach

“…Such an approach has also the advantage of being easy to derive from ocean color remote sensing. This has been showcased in the Mediterranean Sea by the implementation of float-based observational strategies (D'Ortenzio et al, 2020;Le Traon et al, 2020) designed to understand the biological-physical processes driving phytoplankton dynamics in ocean colorderived bioregions (D'Ortenzio and d'Alcala, 2009) (D'Ortenzio et al, 2012). Additionally, selecting regions on the basis of their surface satellite ocean-color characteristics would facilitate the upscaling of regional information, including flux estimates, to the global scale.…”